This thread is purely speculative.
So far the theories I have seen are:
1. ATI wanted to wait to have mainstream/low-end DX10 solutions for a "simultaneous launch".
2. R600's performance sucked compared with the 8800 series, so ATI just threw in the towel.
3. Some kind of crazy bug cropped up at the last minute which made the silicon either very slow or completely unusable, similar to what happened with the X1800.
I'm looking for some more concrete information, but for now I'd enjoy reading some more conspiracy theories.
So far the theories I have seen are:
1. ATI wanted to wait to have mainstream/low-end DX10 solutions for a "simultaneous launch".
2. R600's performance sucked compared with the 8800 series, so ATI just threw in the towel.
3. Some kind of crazy bug cropped up at the last minute which made the silicon either very slow or completely unusable, similar to what happened with the X1800.
I'm looking for some more concrete information, but for now I'd enjoy reading some more conspiracy theories.